By Rex Graham I Nov. 28, 2005

Like millions of other Californians on that morning, Maria Narajo was abruptly awakened on Jan. 17, 1994, by the violent jolts of a 6.7-magnitude earthquake. "It was a boom and my bed was shaking and moving all over the place," said Narajo, who was living at the time on the second floor of a three-story apartment building in Northridge and who spoke Wednesday during a telephone interview from Bishop, CA. "In my living room, the living room wall separated from the window and I could see waves in the swimming pool that looked like they were out in the ocean. We were stuck in our building for a day; we couldn't get out."

In 1994, Narajo worked as a clerk in a seven-story hotel in Van Nuys, which, like her apartment building, was also severely damaged during the earthquake. More than 11 years later, UCSD scientists on Tuesday duplicated ground motions measured at that Van Nuys hotel in the first-ever earthquake shake test of a full-scale section of a 275-ton, mid-rise residential building.

The test of a seven-story structure was the first in a series of planned tests by researchers at the Jacobs School of Engineering that are aimed at evaluating a variety of promising new designs that might improve the earthquake safety of apartment, hotel, and other residential structures in densely populated and seismically active regions in Los Angeles and Southern California. The tests will be performed on a $9 million outdoor "shake table" at UCSD's Englekirk Structural Engineering Center, which is about 8 miles east of the university's main campus. Such full-scale tests have previously not been possible because of weight, space, and technical limitations of smaller indoor shake tables.

"Shear walls" are required by California building codes to be strong enough to support about 30 percent of the building's total weight. However, the test building at UCSD included a shear wall with half the required amount of reinforcing steel, which enabled the building to flex during the test rather remain more rigid.

UCSD's 25- by 40-foot shake table was constructed in September 2004 as part of the National Science Foundation's George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES). The shake table is the largest in the U.S. and the only outdoor shake table in the world, which makes it ideally suited for testing tall, full-scale buildings. Powerful hydraulic actuators can shake a test structure at speeds up to 6 feet per second, a speed that can reproduce near-fault ground motions, creating realistic simulations of the most devastating earthquakes ever recorded. The facility was funded through a grant from the National Science Foundation as well as state, university, and private contributions.

The Nov. 22 test was designed to measure the performance of vertical reinforced concrete structural walls during strong earthquakes. In most of Southern California, structural walls are required by building codes to be strong enough to support about 30 percent of the building's total weight. However, the test building at UCSD included a wall with half the required amount of reinforcing steel in an optimized layout, which offered a high degree of seismic safety for a fraction of the construction cost.

The first floor of the test building showed minor cracks that did not affect the overall structural integrity of the seven-story structure.

"Our computational analyses suggest that shear walls could be designed with significantly less reinforcing steel and still protect life and property during rare, but strong earthquakes," said José Restrepo, a professor of structural engineering at the Jacobs School of Engineering and co-principal investigator of the project. "It may be that we are over-designing some of our buildings with expensive reinforcements that may actually provide very little increase in seismic safety."

The building suffered only very minor cosmetic cracks on a first-floor wall, which Restrepo said was anticipated.

The Nov. 22 earthquake test, which is being supported by a consortium of California engineering and design companies, is an outgrowth of the Jan. 17, 1994, earthquake that resulted in 60 deaths, more than 7,000 injured, 20,000 homeless, and more than 40,000 buildings damaged in Los Angeles, Ventura, Orange, and San Bernardino Counties. There was about $40 billion in property damage. That quake, centered at Northridge, prompted a call by professional structural engineers for more scientific testing of shear walls and other structural elements of mid-rise residential buildings.

"Many people don't realize that excessive building strength can actually promote poor structural performance and non-structural damage during an earthquake," said Robert Englekirk, founder of the center and a co-principal investigator of the project. "The structural engineering community wants to develop regional design procedures that allow for the development of more suitable buildings in Southern California."

Reporters witnessed the dramatic shake test on Nov. 22 at the Englekirk Center.

The building shaken by UCSD researchers is much lighter and less costly to construct that current mid-rise California residential buildings because it has less steel and a smaller foundation. "Our analysis predicts that this lighter building would actually perform better in an earthquake than a heavier structure," said Restrepo.

UCSD engineering researchers plan to build three additional full-scale, steel-reinforced concrete buildings to evaluate other seismic safety systems.

Construction of the seven-story building was made possible through financial support and donated equipment and labor from a consortium of Southern California structural engineering and construction firms.